1. Field of the Invention
This invention, related to the connection device of cables for connection between a vibration wave driven motor and its driving circuit, is used, for example, on the equipment which generates a lot of electro-magnetic noise such as robots etc. Also, the vibration wave driven motor is used on feeble signal detection equipment susceptible to the noise, in the vicinity of such equipment, or at locations away from driving circuits. This invention pertains to the cable connection device of the noise free vibration wave driven motor when used under such circumstances.
2. Related Background Art
On the vibration wave driven motor, a piezo-electric element functioning, as an electro-mechanical energy conversion element is bonded on one side of an elastic member. This piezo-electric element is further provided with plural divided driving phases (electrodes) possessing predetermined phases, driving sensor phases (electrodes) etc. for detecting the vibration state of the elastic member. The driving circuit is connected to each motor phase with a connecting cable and traveling waves are generated on the elastic member by applying AC voltage having a predetermined phase difference at the driving phases.
When a vibration wave driven motor has two driving phases, i.e. A phase and B phase, said connecting cables are provided in two pieces for driving, in one piece for grounding, and in the number of pieces equal to the number of driving detection sensors.
In other words, the grounding cable is used as a common electrode.
However, noise is liable to occur on the connecting cables used to connect the above-mentioned driving circuit to the vibration wave driven motor. As a result, electromagnetic noise or electrostatic noise is often created in the exterior or noise tends to be mixed with the vibration detection signals from the exterior. Further, when the connecting cables are lengthened, there is a possibility of leakage of the AC voltage used for driving, into the vibration detection signals, consequently leading to the following problems.
(1) When the motor is used near intense electro-magnetic noise generating sources such as robots, noise is overlapped on the vibration detection signals resulting in degrading the control performance (wow/flutter stop position accuracy).
(2) Since noise is generated to the exterior, external devices tend to malfunction.
(3) As a result of overlapping of AC voltage for driving onto the vibration detection signals, detection of actual vibration becomes impossible, vibration control performance is degraded, and wow/flutter stop position accuracy drops.
Further, because drive signals are overlapped on potential of the elastic member by current flow through grounding cables, drive signals leak into the devices connected to the vibration wave driven motor and malfunction occurs in external devices.